Drop the Null arm when flattening Nullable<T> into argument variants (#20)

A Nullable<T> argument was fanning out into [T, Null], producing a
`_with_null(val: &Null)` overload everywhere a parameter or setter
accepted `T | null`. The Null overload is API noise: callers either
have a value to pass (use the T arm) or they don't (use an
optional-truncation overload). Forcing them to construct a Null value
just to clear a field offers nothing.

Now Nullable<T> in argument position flattens to [T] only.
Return-position handling (Option<T>, JsOption<T>) is unchanged — that
lives in to_syn_type, independent of this fan-out.

Author: guybedford

CONVENTIONS.md

@@ -60,15 +60,18 @@ borrowed by reference; return-position container types are owned.
 
 ## Optional and nullable types
 
-* `T | null` → `Option<T>` in return position, `Option<T>` in argument
-  position. (`null`-only is rare; treated like `undefined`.)
-* `T | undefined` and `T | null | undefined` → also `Option<T>`. We coalesce
-  at parse time; the rendered union has no separate `null`/`undefined`
-  arm.
+* `T | null` → `Option<T>` in return position. In argument position the
+  `null` arm is dropped — the parameter takes `T` directly. A
+  `_with_null(val: &Null)` overload would force callers to construct a
+  `Null` value with no real upside, and the omission case for
+  truly-optional params is already covered by the optional-truncation
+  rule below.
+* `T | undefined` and `T | null | undefined` follow the same rules as
+  `T | null` — coalesced at parse time; the rendered union has no
+  separate `null`/`undefined` arm.
 * In inner type positions, `T | null` → `JsOption<T>` unless `T` already
   erases to `JsValue`; `JsOption<JsValue>` simplifies to `JsValue`.
-* `T?` on a property → `Option<T>`. The setter takes `Option<T>` too, so
-  callers can clear the property by passing `None`.
+* `T?` on a property → getter returns `Option<T>`; setter takes `T`.
 * `f(x?: T)` (optional parameter) → produces an overload pair, *not* an
   `Option<T>` parameter. See [Signature flattening](#signature-flattening).
 

src/codegen/signatures.rs

@@ -600,15 +600,18 @@ fn flatten_type(ty: &TypeRef, cgctx: Option<&CodegenContext<'_>>, scope: ScopeId
             vec![ty.clone()]
         }
 
-        // Nullable: flatten inner types unwrapped, then add a Null variant.
-        // This expands `T | null` into separate overload variants for each T
-        // plus an explicit `_with_null` variant, rather than wrapping every
-        // alternative in `Option<T>`.
-        TypeRef::Nullable(inner) => {
-            let mut alts = flatten_type(inner, cgctx, scope);
-            alts.push(TypeRef::Null);
-            alts
-        }
+        // Nullable: flatten the inner type, dropping the Null arm.
+        //
+        // Argument-position `Nullable<T>` carries no information that helps
+        // the caller — a `_with_null(val: &Null)` overload is always
+        // useless: callers either have a value to pass (use the `T` arm)
+        // or they don't (use an optional-truncation overload, or the
+        // setter just isn't called). Forcing them to construct a `Null`
+        // value just to clear a field is API noise.
+        //
+        // Return-position handling (`Option<T>` / `JsOption<T>`) is
+        // independent of this fan-out — it lives in `to_syn_type`.
+        TypeRef::Nullable(inner) => flatten_type(inner, cgctx, scope),
 
         // Generic containers are not distributive: `Array<A | B>` and
         // `Record<K, A | B>` are single parameter shapes, not overloads.

tests/snapshots/basic.rs

@@ -65,8 +65,6 @@ extern "C" {
     #[wasm_bindgen(constructor, catch, js_name = "Response")]
     pub fn new_with_form_data(body: &FormData) -> Result<Response, JsValue>;
     #[wasm_bindgen(constructor, catch, js_name = "Response")]
-    pub fn new_with_null(body: &Null) -> Result<Response, JsValue>;
-    #[wasm_bindgen(constructor, catch, js_name = "Response")]
     pub fn new_with_readable_stream_and_init(
         body: &ReadableStream,
         init: &ResponseInit,
@@ -90,8 +88,6 @@ extern "C" {
         body: &FormData,
         init: &ResponseInit,
     ) -> Result<Response, JsValue>;
-    #[wasm_bindgen(constructor, catch, js_name = "Response")]
-    pub fn new_with_null_and_init(body: &Null, init: &ResponseInit) -> Result<Response, JsValue>;
     #[doc = " Returns a new Response with a network error."]
     # [wasm_bindgen (static_method_of = Response)]
     pub fn error() -> Response;

tests/snapshots/cloudflare-worker.rs

@@ -147,8 +147,6 @@ extern "C" {
     pub fn set_body_with_url_search_params(this: &RequestInit, val: &URLSearchParams);
     #[wasm_bindgen(method, setter, js_name = "body")]
     pub fn set_body_with_form_data(this: &RequestInit, val: &FormData);
-    #[wasm_bindgen(method, setter, js_name = "body")]
-    pub fn set_body_with_null(this: &RequestInit, val: &Null);
     #[wasm_bindgen(method, getter)]
     pub fn redirect(this: &RequestInit) -> Option<String>;
     #[wasm_bindgen(method, setter)]
@@ -212,10 +210,6 @@ impl RequestInitBuilder {
         self.inner.set_body_with_form_data(val);
         self
     }
-    pub fn body_with_null(self, val: &Null) -> Self {
-        self.inner.set_body_with_null(val);
-        self
-    }
     pub fn redirect(self, val: &str) -> Self {
         self.inner.set_redirect(val);
         self
@@ -250,8 +244,6 @@ extern "C" {
     #[wasm_bindgen(constructor, catch, js_name = "Response")]
     pub fn new_with_form_data(body: &FormData) -> Result<Response, JsValue>;
     #[wasm_bindgen(constructor, catch, js_name = "Response")]
-    pub fn new_with_null(body: &Null) -> Result<Response, JsValue>;
-    #[wasm_bindgen(constructor, catch, js_name = "Response")]
     pub fn new_with_readable_stream_and_init(
         body: &ReadableStream,
         init: &ResponseInit,
@@ -275,8 +267,6 @@ extern "C" {
         body: &FormData,
         init: &ResponseInit,
     ) -> Result<Response, JsValue>;
-    #[wasm_bindgen(constructor, catch, js_name = "Response")]
-    pub fn new_with_null_and_init(body: &Null, init: &ResponseInit) -> Result<Response, JsValue>;
     # [wasm_bindgen (static_method_of = Response)]
     pub fn redirect(url: &str) -> Response;
     # [wasm_bindgen (static_method_of = Response , catch , js_name = "redirect")]

tests/snapshots/coverage.rs

@@ -212,8 +212,6 @@ extern "C" {
     pub fn next(this: &LinkedList) -> Option<LinkedList>;
     #[wasm_bindgen(method, setter)]
     pub fn set_next(this: &LinkedList, val: &LinkedList);
-    #[wasm_bindgen(method, setter, js_name = "next")]
-    pub fn set_next_with_null(this: &LinkedList, val: &Null);
 }
 impl LinkedList {
     pub fn new(data: &JsValue, next: Option<&LinkedList>) -> LinkedList {
@@ -408,8 +406,6 @@ extern "C" {
     pub fn set_body(this: &FetchOptions, val: &str);
     #[wasm_bindgen(method, setter, js_name = "body")]
     pub fn set_body_with_array_buffer(this: &FetchOptions, val: &ArrayBuffer);
-    #[wasm_bindgen(method, setter, js_name = "body")]
-    pub fn set_body_with_null(this: &FetchOptions, val: &Null);
     #[wasm_bindgen(method, getter)]
     pub fn redirect(this: &FetchOptions) -> Option<String>;
     #[wasm_bindgen(method, setter)]
@@ -453,10 +449,6 @@ impl FetchOptionsBuilder {
         self.inner.set_body_with_array_buffer(val);
         self
     }
-    pub fn body_with_null(self, val: &Null) -> Self {
-        self.inner.set_body_with_null(val);
-        self
-    }
     pub fn redirect(self, val: &str) -> Self {
         self.inner.set_redirect(val);
         self

tests/snapshots/node-console.rs

@@ -19,16 +19,12 @@ pub mod console {
         pub fn stderr(this: &ConsoleOptions) -> Option<Object>;
         #[wasm_bindgen(method, setter)]
         pub fn set_stderr(this: &ConsoleOptions, val: &Object);
-        #[wasm_bindgen(method, setter, js_name = "stderr")]
-        pub fn set_stderr_with_null(this: &ConsoleOptions, val: &Null);
         #[doc = " Ignore errors when writing to the underlying streams."]
         #[doc = " @default true"]
         #[wasm_bindgen(method, getter, js_name = "ignoreErrors")]
         pub fn ignore_errors(this: &ConsoleOptions) -> Option<bool>;
         #[wasm_bindgen(method, setter, js_name = "ignoreErrors")]
         pub fn set_ignore_errors(this: &ConsoleOptions, val: bool);
-        #[wasm_bindgen(method, setter, js_name = "ignoreErrors")]
-        pub fn set_ignore_errors_with_null(this: &ConsoleOptions, val: &Null);
         #[doc = " Set color support for this `Console` instance."]
         #[doc = " @default 'auto'"]
         #[doc = ""]
@@ -39,16 +35,12 @@ pub mod console {
         pub fn set_color_mode(this: &ConsoleOptions, val: bool);
         #[wasm_bindgen(method, setter, js_name = "colorMode")]
         pub fn set_color_mode_with_str(this: &ConsoleOptions, val: &str);
-        #[wasm_bindgen(method, setter, js_name = "colorMode")]
-        pub fn set_color_mode_with_null(this: &ConsoleOptions, val: &Null);
         #[doc = " Set group indentation."]
         #[doc = " @default 2"]
         #[wasm_bindgen(method, getter, js_name = "groupIndentation")]
         pub fn group_indentation(this: &ConsoleOptions) -> Option<f64>;
         #[wasm_bindgen(method, setter, js_name = "groupIndentation")]
         pub fn set_group_indentation(this: &ConsoleOptions, val: f64);
-        #[wasm_bindgen(method, setter, js_name = "groupIndentation")]
-        pub fn set_group_indentation_with_null(this: &ConsoleOptions, val: &Null);
     }
     impl ConsoleOptions {
         pub fn new(stdout: &Object) -> ConsoleOptions {
@@ -68,18 +60,10 @@ pub mod console {
             self.inner.set_stderr(val);
             self
         }
-        pub fn stderr_with_null(self, val: &Null) -> Self {
-            self.inner.set_stderr_with_null(val);
-            self
-        }
         pub fn ignore_errors(self, val: bool) -> Self {
             self.inner.set_ignore_errors(val);
             self
         }
-        pub fn ignore_errors_with_null(self, val: &Null) -> Self {
-            self.inner.set_ignore_errors_with_null(val);
-            self
-        }
         pub fn color_mode(self, val: bool) -> Self {
             self.inner.set_color_mode(val);
             self
@@ -88,18 +72,10 @@ pub mod console {
             self.inner.set_color_mode_with_str(val);
             self
         }
-        pub fn color_mode_with_null(self, val: &Null) -> Self {
-            self.inner.set_color_mode_with_null(val);
-            self
-        }
         pub fn group_indentation(self, val: f64) -> Self {
             self.inner.set_group_indentation(val);
             self
         }
-        pub fn group_indentation_with_null(self, val: &Null) -> Self {
-            self.inner.set_group_indentation_with_null(val);
-            self
-        }
         pub fn build(self) -> ConsoleOptions {
             self.inner
         }